1. Field of the Invention
The present invention relates to a rotary electric machine, and more particularly to a rotary electric machine which is preferable for a structure employing a noise countermeasure.
2. Description of Related Art
Since the rotary electric machine is generally rotated at a high speed such as 3000 rpm or 3600 rpm, a very loud noise is generated. Accordingly, various artifices are employed as the noise countermeasure.
Particularly, in the case that a noise control is severe, a countermeasure is carried out in such a manner as to surround a whole of the rotary electric machine by a noise insulation enclosure so as to control noise and keep a noise control value in an outer side of the noise insulation enclosure, as described in JP-A-5-219683. Further, as a noise countermeasure against a general noise control, there is a countermeasure that an internal sound is reduced by installing an acoustic absorbent in an inner side of a stator frame so as to intend to reduce the noise, as described in JP-A-11-252850. Further, as the other noise countermeasure, a noise value is reduced by increasing a thickness of the stator frame.
However, if the whole of the rotary electric machine is surrounded by the noise insulation enclosure as mentioned above, there is a problem that a space for installing the noise insulation enclosure is necessary around the rotary electric machine, and a base for installing the noise insulation enclosure is necessary. Since the noise insulation enclosure reduces the noise in an outer portion of the noise insulation enclosure, however, does not reduce the noise in an inner portion of the noise insulation enclosure, it is necessary for an inspection worker to enter into the enclosure, for example, in the case of inspecting the rotary electric machine, and there is a risk that the inspecting worker entering into the noise insulation enclosure is exposed to a loud noise of the rotary electric machine. In addition, within the noise insulation enclosure, since the surface of the stator frame becomes high temperature at a time of operating the rotary electric machine, there is a problem that the temperature within the noise insulation enclosure is increased. Further, since the noise insulation enclosure is sufficiently shielded and sealed for noise insulation, there is a risk that a lack of oxygen is generated. In order to prevent these problems, it is necessary to be provided with a ventilating equipment. Further, a firefighting equipment is necessary within the noise insulation enclosure for safety reasons, and the incidental equipment of the noise insulation enclosure is large scaled.
On the other hand, in the case that an acoustic absorbent is attached to an inner side of the stator frame, the acoustic absorbent becomes fragile due to an aged deterioration of the acoustic absorbent, the acoustic absorbent flies in all directions due to an inside wind generated at a time of operating the rotary electric machine, and there is a risk of affecting a cooling performance of the rotary electric machine. Further, it is necessary to structure such that the acoustic absorbent is fixed to the stator frame for attaching the acoustic absorbent, and there is a problem that the structure of the stator frame is complicated.
Further, in the case that the thickness of the stator frame is made thick, there is a problem that a weight of a power generator is increased by increasing the thickness.